1. Field of the Invention
The present invention generally relates to a switching regulator circuit (hereinafter referred to as SW regulator circuit) constructed of a simple circuit and operable in a high efficiency. More specifically, the present invention is directed to such a switching regulator circuit capable of eliminating a recharging operation of a power supply by a reverse current flowing through a coil.
2. Description of the Related Art
FIG. 8 shows a circuit diagram of a switching regulator circuit typically known as a conventional step-up type SW (switching) regulator circuit. In this step-up type SW regulator circuit, a power supply 10 is connected to one end of a coil 11, whereas both a switch element (hereinafter referred to as SW element) 13 and a diode 12 are connected to the other end of this coil 11. The other end of the diode 12 constitutes an output terminal of the SW regulator circuit. To this output terminal, both a capacitor 14 and a load 15 are connected, while an SW regulator control circuit 20 controls ON time and OFF time of the SW element 13 in order that the output voltage of the output terminal becomes a certain constant voltage "Vout". In the SW regulator circuit of FIG. 8, since a current flows through the diode 12, a loss occurs. To reduce this loss, as shown in FIG. 9, such a synchronous rectifying type SW regulator is conducted in which another SW element 16 is additionally connected parallel to the diode 12, and both the SW element 13 and the SW element 16 are operated in a complementary mode as represented in FIG. 10. As a result, generally speaking, a converting efficiency of a synchronous rectifying type SW regulator can be increased by approximately 5%.
In this synchronous rectifying type SW regulator, the current of the coil 11 flows via the SW element 16 along the reverse direction in the current mode other than the current continuous mode (namely, in current discontinuous mode where coil current is reduced to 0), so that this reverse coil current charges the power supply 10 which may cause a problem. This SW element 16 is connected parallel to the diode 12.